In the electrical power distribution field, draw-out type voltage circuit breakers are quite large and are usually housed in corresponding circuit breaker cells of switchgear. Since such large circuit breakers may be installed in energized circuit breaker cells, it is preferred that some form of remote electrical means be employed for the installation process so that personnel performing the installation operation can be positioned several tens of feet away from the energized equipment. For this purpose, some mechanical means, such as racking devices, are employed to engage ("rack-in") or withdraw these large circuit breakers into or from contact with the electrical power conductors located at the rear of the switchgear cells.
Racking-in or withdrawing a circuit breaker is typically accomplished using a detachable hand crank which is inserted into a circuit breaker racking mechanism having cooperative cranks and gearing which moves the circuit breaker within the cell as a function of turning the crank. Typically, the crank moves horizontally with the circuit breaker as it moves in and out of the cell. When the operation is complete the crank is removed from the circuit breaker and used on other circuit breakers or placed into storage. Racking-in or withdrawing of the circuit breaker is typically done with the circuit breaker access door of the switchgear cell open. However, in applications where enhanced personnel protection is desired, it is sometimes required that the circuit breaker be racked-in or out with the door closed. In these cases, the access door is closed and the hand crank is inserted through a hole in the door. As the circuit breaker moves, the crank moves in and out of the hole in the door with the movement of the circuit breaker.
Where it is necessary to have a remote electric racking device that will perform the above-described tasks, traditional racking device designs are too complex and cannot be implemented economically. Hence, there is a need for a racking assembly of the above kind which can be remote controlled, can be economically implemented that is easier to use and provides additional safety to the operator. Additionally, remote controlled racking assemblies require an anti-rotation means for preventing the racking assembly from rotating when the circuit breaker is being racked in.
Such an electric racking device should fulfill at least four requirements: 1) the remote racking device should be able to be moved from one circuit breaker cell to another without requiring the permanent mounting of a motor in each switchgear cell or each circuit breaker; 2) when the electric racking device is connected to the moving circuit breaker, it must move horizontally with the circuit breaker as it moves; 3) the electric racking device should be attachable to the outside of the cell door such that once the cell door is closed it can always remain closed after the circuit breaker is placed into the desired position and 4) the device should be designed such that it can be used with switchgear equipment already in service with minimum retrofitting expense.